The shell mold process, the hot box process or warm box process (hereinafter referred to as "the hot box process or the like") and the normal-temperature acid-hardening process are widely utilized today as a valuable mold-forming method. Since different materials suitable for these methods are used therefor, respectively, each method has inherent problems resulting from the material used.
In the shell mold process, since a phenolic resin is mainly used as the binder, when a low-melting-point metal such as an aluminum alloy or a magnesium alloy is cast, the core retains a high strength even after casting, because of a high heat resistance of the phenolic resin. Accordingly, to discharge the residual sand from the cast product, shocks are imposed by a chipping machine, or the operation of heat-treating the cast product in a heating furnace at 400 to 500.degree. C. for several hours to thermally decompose the binder of the residual core sand for removal thereof is carried out. Therefore, a great deal of labor and a large amount of energy are necessary. Furthermore, since a phenolic resin is mainly used, the mold-forming temperature is high, in the range of from 250 to 350.degree. C., and to reduce the energy cost, improve the working environment, prolong the life of the metal mold, and improve the freedom of the metal mold design for increasing the precision of the core, a reduction of the mold-forming temperature is desired. At present, however, a mass production of molds at temperatures lower than 200.degree. C. is very difficult.
In the hot box process or the like, since an acidic compound is used as the hardener for a binder represented by a furan type compound and the sand is in the wet state, the metal mold is easily corroded and the pot life of the molding material is generally short, whereby the mold-forming operation is impeded.
In the normal-temperature acid-hardening process, an acid is used as the hardener as in the hot box process or the like, but since an organic sulfonic acid type is mainly used, a harmful gas such as sulfurous acid gas is generated when casting a metal, to cause a problem such as contamination of the working environment.
Therefore, an object of the present invention is to provide a novel material for a mold, which is hardened at normal temperature or a relatively low temperature, does not cause corrosion of a metal mold or contamination of the working environment, and manifests an excellent disintegrability of a formed mold and a good pot life, and a method of forming a mold by using this material.